1. Field of the Invention
This invention relates to a hose joint. More particularly, it is concerned with a joint structure defined between a hose for, for example, an automotive fuel or lubricant line and a joint provided on one end of a connecting pipe and having an outer nipple surface covered by a thermosetting resin layer.
2. Description of the Prior Art
A conventional hose for a fuel line is fragmentarily shown at 1 in FIG. 1 by way of example. The hose 1 comprises an inner tube 2 formed from fluorine rubber (FKM) or a mixture of acrylonitrile-butadiene rubber and polyvinyl chloride (NBR/PVC), a reinforcing layer 3 formed from braided vinylon, polyester, polyamide, rayon or aromatic polyamide fiber and surrounding the inner tube 2, and an outer tube 4 formed from epichlorohydrin rubber (CHC), chlorosulfonated polyethylene rubber (CSM), chlorinated polyethylene rubber (CPE), acrylic rubber (ACM) including a copolymer of ethylene, vinyl acetate and acrylic ester, or chloroprene rubber (CR) and surrounding the reinforcing layer 3. The inner tube 2, reinforcing layer 3 and outer tube 4 are joined to one another by an adhesive. Another conventional hose is shown at 1 in FIG. 2, and includes an inner tube 2 which consists of an inner layer 2' and an outer layer 2". The inner layer 2' is formed from the same material as that from which the inner tube 2 in the hose of FIG. 1 is formed. The outer layer 2" is formed from acrylonitrilebutadiene rubber (NBR), epichlorohydrin rubber, acrylic rubber including a copolymer of ethylene, vinyl acetate and acrylic ester, chlorosulfonated polyethylene rubber or chlorinated polyethylene rubber. The inner and outer layers 2' and 2" are joined together by vulcanization. The hose 1 also includes a reinforcing layer 3 and an outer tube 4 which are formed from the same material as those from which the reinforcing layer 3 and the outer tube 4 in the hose of FIG. 1 are, respectively, formed. The inner tube 2, reinforcing layer 3 and outer tube 4 are joined to one another by an adhesive. These hoses are disclosed in U.S. Pat. No. 4,330,017 to Satoh et al. and U.S. Pat. No. 3,944,453 to Chudgar et al., respectively.
A hose of such construction is connected to a hose joint provided on one end of a connection pipe. There is known a hose joint having a nipple which carries an adhesive layer on its outer peripheral surface. The nipple is inserted into one end of the hose, and a sleeve is placed around the hose end. The sleeve is caulked, whereby the hose end is tightly held between the nipple and the sleeve. The hose and the nipple are joined to each other by the adhesive layer provided on the outer surface of the nipple. This joint structure provides a satisfactory seal which prevents the leakage of a fluid, such as fuel oil or lubricant, through the boundary between the hose and the nipple. It has, however, a number of drawbacks, too, as will hereinafter be pointed out.
This joint structure essentially requires the adhesion between the inner surface of the hose end and the outer surface of the nipple. The adhesion usually requires a special step, whether it may be carried out at an ambient or elevated temperature. A lot of labor and cost are required for the selection of an appropriate adhesive, its quality control and the control for the entire process for the production of the hose joints. More specifically, it is necessary to choose an appropriate adhesive which suits the material of a particular hose. It is most advisable to employ an adhesive (or rubber cement) which consists of the same material as the innermost layer of the hose, for example, an adhesive (or rubber cement) consisting of an acrylonitrile-butadiene rubber composition for a hose having an inner tube (2 in FIG. 1) or inner layer (2' in FIG. 2) formed from an acrylonitrile-butadiene rubber composition, or an adhesive (or rubber cement) consisting of a fluorine rubber composition for a hose having an inner tube or layer formed from a fluorine rubber composition. Various kinds of adhesives (or rubber cements) are, therefore, required. Moreover, it is usually necessary to use a primer, since those adhesives (or rubber cements) are unsuitable for bonding a rubber hose direcly to a nipple which is usually made of steel. Thus, a lot of money and labor are required for the quality control of the adhesives and the primers and the control for the entire production process.
In the event the step of adhesion involves heating, it is likely to give to a number of problems, including the deterioration of the reinforcing fiber layer 3 which is usually disposed between the inner and outer tubes 2 and 4 of the hose 1, and the failure to obtain any acceptable adhesive strength as a result of the separation of the adhesive layer from the outer surface of the nipple when it is inserted into the hose.
Moreover, it is likely that the hose may be inadvertently separated from the joint during regular inspection or repairs after certain periods of use on an automobile, especially if the hose is clamped to the joint. In any such event, it is no longer possible to recover any satisfactory connection, even if the joint may be inserted into the hose. Thus, it has hitherto been impossible to obtain any maintenance-free hose joint structure.